Hydrotalcite particles have been developed as a stabilizer to prevent the halogen and/or acidic substance contained in the following substances from causing the corrosion or formation of rust in metal portions of a molding machine or a metal mold at the time of molding or causing, in particular, such a trouble that the obtained resin or a molded article thereof deteriorates by heat or ultraviolet light (for example, U.S. Pat. No. 4,347,353 and JP-B 58-46146). The substances are halogen-containing polyolefins (used as a general term for homopolymers as well as various copolymers in the present invention) derived from a polymerization catalyst and/or post-halogenation such as olefin polymers and copolymers thereof, produced by a Ziegler polymerization catalyst which comprises a halogen-containing compound as a catalyst component and/or carrier component, and chlorinated polyethylene; halogen- and/or acidic substance-containing thermoplastic resins such as AS, ABS, polyacrylates and polymethacrylates produced using a catalyst containing halogen and/or an acidic substance such as sulfuric acid, boron trifluoride, tin tetrachloride or hydrochloric acid; halogen-containing thermoplastic resins such as polymer blends containing vinylidene chloride polymers and copolymers and a vinyl chloride resin; halogen-containing thermoplastic resins such as chlorinated vinyl chloride polymers and copolymers; and thermoplastic resins containing halogen and/or an acidic substance derived from a catalyst and/or monomer and/or post-halogenation such as blend resins containing these.
Although the above hydrotalcite particles have properties suitable for giving a molded article having excellent heat deterioration resistance when contained in a resin, it has been found that the hydrotalcite particles still have problems to be solved along with recent growing requirements for the properties of the particles in spite of the fact that the amount of the hydrotalcite particles to be contained in a resin is very small.
That is, it has been strongly demanded that the hydrotalcite particles have excellent stability against heat and ultraviolet light for resins.
Then, the inventors of the present invention have conducted further studies to meet this demand and have found that the amounts of specific metal compounds as impurities contained in the hydrotalcite particles and the shape of the particle have influence upon heat deterioration and physical properties and that an excellent heat deterioration resisting agent can be obtained by limiting these to specific values.
Although the hydrotalcite particles as a resin additive are produced in large quantities on an industrial scale, various impurities derived mainly from their source materials are contained in the hydrotalcite particles in the production process of the hydrotalcite particles as a solid solution or impurity.
That is, the hydrotalcite particles are industrially produced from a magnesium source material, aluminum source material and alkali source material as main source materials, and these source materials mostly rely on natural resources or processed products thereof. Therefore, these source materials contain many kinds of metal compounds and non-metal compounds and are refined for use in limits that costs permit. It is, however, impossible to avoid the inclusion of many kinds of impurities.
In the production process of the hydrotalcite particles, the elution and inclusion of metals derived from the materials of various apparatuses such as a reactor, container, transport pipes, crystallizer or grinder cannot be avoided completely.
The present inventors have identified components which have an influence upon heat deterioration and reductions in properties at the time of molding a resin or upon the heat deterioration of a molded article, out of many kinds of impurities which are contained in hydrotalcite and derived from its source materials and included during its production process, and have conducted studies on the components and the amounts thereof. They have found that when an iron compound and a manganese compound out of various impurities are contained even in trace amounts as an impurity or a solid solution, they have influence upon the heat deterioration of a resin.
It has also been found with regard to the hydrotalcite particles of the present invention that the total content of these specific impurities is limited to values smaller than predetermined values in order for these specific impurities to exert a marked function on heat deterioration and that the particle diameter and specific surface area of the hydrotalcite particle also have influence upon heat deterioration. Therefore, it has been revealed that, to obtain a composition which rarely deteriorates by heat when contained in a resin, (i) the amounts of specific metal compounds contained in the hydrotalcite particles should be smaller than or equal to predetermined values, (ii) the average secondary particle diameter of the hydrotalcite particles should be smaller than or equal to a predetermined value (that is, the particles rarely agglomerate), and (iii) the hydrotalcite particles should have a predetermined specific surface area (or a good crystal form).